Between
9 and 11 hours per week, depending
on your approach to your problem.

Complete
Solution:

There are many ways to do this problem.
The answer can only be approximated
because of the way the data are reported.

If you assume that the table
shows data for 100 students, then the 7% who
worked from one to five hours would correspond to seven
students who worked one to five hours. To find an average
(mean), you need to estimate the total number of hours
worked. Consider the seven students who worked from one
to five hours. Taken together, the
least time they could have worked is seven hours.
The greatest they could have worked is 35 hours.
(The actual number is probably somewhere in between these
values.) The first chart shows the least number of hours
the 100 students could have worked, while the second chart
shows the greatest number of hours they could have worked.

Least
Number of Hours

Number
of Students1

Least
Number of Total Hours

0

36

0

1

7

7

6

9

54

11

11

121

16

17

272

21

21

441

Total

100

895

Greatest
Number of Hours

Number
of Students1

Least
Number of Total Hours

0

36

0

5

7

35

10

9

90

15

11

165

20

17

340

251

21

525

Total

100

1155

1estimated

To find the lower value for
the average number of hours worked per week,
divide the total number of hours by the number of students:
895 ÷ 100 = 8.95. The larger value for the average
workweek can be foud in the same way: 1155 ÷ 100
= 11.55. Using this approach, an estimate for the average
for a high school senior is between 8.5 and 12.5 hours.

Another way to estimate
the average uses an average for
the hours worked in each category.

Smallest
Number of Hours

Largest
Number of Hours

Average
Number of Hours

Number
of Students1

Total
Hours Worked

0

0

0

36

0

1

5

3

7

21

6

10

8

9

72

11

15

13

11

143

16

20

18

17

306

21

251

23

21

483

Total

100

1025

1estimated

To find a value for the average, divide
the total number of hours by the number of students:
1025 ÷ 100 = 10.25. This method results in an average
of about 10 and 1/4 hours.